The present invention relates to a magnetic video tape recording and reproducing apparatus having rotary heads. In particular, it relates to a so-called traverse scanning type video tape recorder which has a plurality of magnetic video heads rotating in a direction substantially perpendicular to the direction of tape travel and in which a magnetic tape is scanned in a direction perpendicular to the direction of tape motion by the rotary heads so as to record or reproduce signals.
Hitherto, magnetic video recording and reproducing apparatus having four rotary video heads or helical scanning type magnetic video recording and reproducing apparatus having two rotary video heads have been employed for broadcasting, industrial or domestic use.
Recently, these magnetic video tape recording and reproducing apparatus, i.e. VTR have become compact. For instance, the smallest broadcasting use VTR having four heads weighs about 24 Kg, and the smallest oblique scanning type VTR weighs about 18-25 Kg. In the two-head helical scanning type VTR, the relative speed between tape and head is determined to be around 10 m/sec, since the signal within one field of the standard television signal is recorded on one track and the size of the apparatus is limited. Accordingly, recording of the high frequency components of a television signal is insufficient. Especially, in the case of a color television signal, the VTR of this kind is not suitable for broadcasting use. In addition, this VTR has such disadvantages as large jitter and difficulty in splice editing of recorded magnetic tape. In comparison with the two-head VTR, the four-head VTR of the type mentioned above does not have the disadvantages of the two-head VTR. It is, however, difficult to make the four-head VTR more compact, because the tape path requires a comparatively long canoe area in which the tape is gradually curved to hold the same to a female guide, and in the case of the usual tape having a tape width of 2 inches, the canoe area should be sufficiently long. When high density recording is desired and the recording video track width is set at a quarter of the normal width, the use of the normal tape having a tape width of 2 inches results in a decrease of the tape travelling speed to a quarter of the normal speed, and therefore the recording and reproducing characteristics of the audio signal is largely deteriorated.
The conventional VTR, which has rotary heads to record and reproduce a video signal, has rotary transformers. In this case, it is necessary to provide the same number of rotary transformers, recording amplifiers, reproducing pre-amplifiers and equalizers as the number of rotary heads, so that the increase in the number of rotary heads makes it difficult to realize a more compact, lighter and low power consumption VTR.
In the conventional VTR, a sinusoidal wave signal (240 Hz in the case of the four-head VTR) which is required to improve the tape tracking accuracy of the rotary head during the reproducing or playback mode is combined with a frame sync signal (30 Hz) in a form of a pulse for phase locking the reproduced picture with an external sync signal so as to produce a control signal which is recorded on the magnetic tape. In the reproducing mode, both the sinusoidal wave signal and the frame sync signal are separated from the reproduced signal. In this case, these signals are separated by a band pass filter in the reproducing mode, so that the band width of a tape travelling servo loop including the band pass filter becomes narrow and at the same time the phase characteristics in the higher frequency range are deteriorated. Therefore, it is difficult to increase the loop gain, so that the tape travelling jitter cannot be sufficiently suppressed and an increase in the tracking accuracy cannot be expected. In addition, in order to realize a high density magnetic record by means of narrow-width video heads, it is necessary to improve the tracking accuracy by increasing the frequency of the control signal almost up to the critical frequency of recording. The conventional multi-recording in the above mentioned pulse form does not satisify this requirement, and it has been desired to develop a new multi-recording system.
Further, the conventional VTR has a control signal track at the side end portion of the magnetic tape. In this case, this tape portion is more expansible than the center portion. The tape is curved to fit a circular path of the video head so that the tape is apt to change its shape. Therefore, the relative phase between the control track and the video track is varied, and the reproducing level of the control signal is varied, so that tracking error occurs. The thinner the tape and the shorter the recording wavelength of the control signal on the control track, the more sufficient the above influences become. Therefore, these influences are an obstacle to the realization of high density recording by utilizing a thin tape and narrow width track.
There is also a further disadvantage in the prior conventional VTR. in that, the capstan servo system for controlling tape travel has a simple integral control or a combination of integral and local proportional controls so that jitter is apt to occur due to the lack of uniform tape travel.